FIG. 1 is a structural diagram illustrating a network structure of an Evolved Universal Mobile Telecommunications System (E-UMTS) which is called a fourth-generation mobile communication system. The E-UMTS system is developed from a conventional UMTS system, and conducts intensive research into a basic standardization process in the current 3GPP. The E-UMTS system may also be called a Long Term Evolution (LTE) system.
The E-UMTS network is classified into an Evolved UTRAN (E-UTRAN) and an Evolved Packet Core (EPC). The E-UMTS includes a user equipment (UE), an eNode-B and an Access Gateway (AG) which is located at the end of a network and connected to an external network. The AG may be called as a Mobility Management Entity (MME)/User Plane Entity (UPE). The AG may be divided into a first AG part for taking charge of user traffic and a second AG part for taking charge of control traffic. In this case, a new interface may be located between the first AG part for processing the user traffic and the second AG part for processing the control traffic, such that the first AG part may communicate with the second AG part. A single eNode-B may include at least one cell. An interface for transmitting either the user traffic or the control traffic may be used between the eNode-Bs. The EPC may include an AG and a node for user registration of UEs. An interface for distinguishing the E-UTRAN from the EPC may also be used. The eNode-Bs and the AG may be connected via an S1 interface. In this case, the several nodes are interconnected (i.e., Many to Many Connection). The eNode-Bs may be connected to each other via an X2 interface, and have a meshed network structure with the X2 interface.
Radio protocol layers between the user equipment (UE) and the network are classified into a first layer (L1), a second layer (L2), and a third layer (L3) based on an Open System Interconnection (OSI) reference model well known to a communication system. A physical layer, the first layer (L1), provides an information transfer service using a physical channel. A radio resource control (RRC) layer located in a third layer controls radio resources between the UE and the network. For this operation, the RRC message is exchanged between the UE and the network. The RRC layer is located at the eNode-B in the E-UTRAN.
FIG. 2 is a structural diagram illustrating a radio protocol layer structure between the UE and the E-UTRAN (Evolved-UMTS Terrestrial Radio Access Network) on the basis of the 3GPP radio access network standard specification of the third-generation mobile communication standardization organization. The radio protocol layer structure of FIG. 2 horizontally includes a physical layer, a data link layer, and a network layer. The radio protocol layer structure of FIG. 2 vertically includes a user plane for transmitting data and a control plane for transmitting a control signal (i.e., signaling information). The radio protocol layers of FIG. 2 are classified into a first layer (L1), a second layer (L2), and a third layer (L3) based on an Open System Interconnection (OSI) reference model well known to a communication system.
The control plane and the user plane in the radio protocol layer structure of FIG. 2 will hereinafter be described. The first layer (L1) is a physical layer. The physical layer provides an upper layer with an information transfer service through a physical channel. The physical layer is connected to a medium access control (MAC) layer located at a higher level through a transport channel. Data is transferred between the MAC layer and the physical layer via the transport channel. Data is transferred between different physical layers through a physical channel. Between different physical layers, namely, between physical layers of a transmission side and a reception side, data is transferred via the physical channel.
The medium access control (MAC) layer of the second layer provides services to a radio link control (RLC) layer located at a higher level through a logical channel. The RLC layer supports the transmission of data with reliability. It should be noted that the RLC layer illustrated in FIG. 2 is depicted because if the RLC functions are implemented in and performed by the MAC layer, the RLC layer itself is not required. The PDCP layer of the second layer (L2) performs a header compression function for reducing the IP packet header size including relatively large- and unnecessary-control information, such that it can effectively transmit IP packet (such as IPv4 or IPv6) within a narrow-bandwidth RF interval. The PDCP layer of the E-UTRAN may be located at the AG.
A Radio Resource Control (RRC) layer located at the lowest portion of the third layer is only defined in the control plane. The RRC layer is associated with configuration, re-configuration, and release of a radio bearer (RB), such that it controls logical channels, transport channels, and physical channels. In this case, the radio bearer (RB) signifies a service provided by the second layer for data communication between the UE and the E-UTRAN.
The unit of data transferred to each layer of the radio protocol layer structure is called different names. This data unit is called a service data unit (SDU). A basic unit for allowing a protocol layer to transfer data to another protocol layer is called a protocol data unit (PDU). Data which is transferred between layers of a radio access protocol structure or between radio access protocol structures signifies a predetermined data block such as the above-mentioned SDU or PDU.
FIG. 3 is a flow chart illustrating a procedure for an RRC connection in the E-UMTS system. In order to establish a call connection between the UE and the E-UTRAN system, the UE must establish a RRC connection with the E-UTRAN system, and must also establish a signaling connection with a Core Network (CN). In order to disclose detailed operations of the above RRC connection and the above signaling connection, a RRC state of the UE and the RRC connection procedure will hereinafter be described in detail. The RRC state indicates whether the RRC layer of the UE is logically connected to the RRC layer of the E-UTRAN. If it is determined that the RRC layer of the UE is logically connected to the RRC layer of the E-UTRAN, this state is called a RRC connected state. If the RRC layer of the UE is not logically connected to the RRC layer of the E-UTRAN, this state is called a RRC idle state. A UE in the RRC connected state has a RRC connection with the E-UTRAN, such that the E-UTRAN can recognize the presence of the corresponding UE in a cell. As a result, the UE can be effectively controlled. Otherwise, a UE in the RRC idle state cannot be recognized by the E-UTRAN, but is controlled by a core network (CN) in a tracking area larger than the cell. In other words, only the presence or absence of the above UE in the RRC idle state is recognized in the unit of a large region. If the UE in the RRC idle state desires to receive a mobile communication service such as a voice or data service, the UE must transit to the RRC connection state. Associated detailed description will hereinafter be described in detail.
If a user initially powers on his or her UE, the UE searches for an appropriate cell, and stays in a RRC idle state in the searched cell. The UE staying in the RRC idle state establishes a RRC connection with the RRC layer of the E-UTRAN through a RRC connection procedure when the UE needs to establish the RRC connection, such that the UE transits to the RRC connection state. The UE in the RRC idle state must establish the RRC connection with the E-URTAN due to a variety of reasons. For example, if uplink data transmission is needed due to a user's phone call attempt, or if a paging message is received from the E-UTRAN such that a response message for the paging message must be transmitted, the UE in the RRC idle state needs to connect the RRC connection with the E-URTAN. By means of the RRC connection and the signaling connection, the UE exchanges UE-dedicated control information with the E-UTRAN or CN.
As shown in FIG. 3, according to a first process for the RRC connection establishment, the UE transmits a RRC connection request message to a base station (BS) at step S310. The base station is located at the last end of the E-UTRAN, and wirelessly transmits/receives data to/from the UE. For the convenience of description, the base station to be disclosed in the following description is indicative of the E-UTRAN.
In order to response the RRC connection request message, the base station transmits the RRC connection setup message to the UE at step S320.
The UE transmits the RRC connection setup complete message to the base station at step S330. If the above-mentioned process has been successfully completed, the RRC connection is established between the UE and the base station.
After the RRC connection has been established, the UE initiates a process for establishing the signaling connection by transmitting an initial direct transfer (IDT) message at step S340.
In the meantime, the base station may establish a UE-dedicated physical channel for only one UE. The UE can transmit Layer1/Layer2 (L1/L2) control information to the base station using the above UE-dedicated physical channel. There is a variety of L1/L2 control information, for example, control information to request a scheduling message from the UE to the base station, reference information for the base station to measure a quality of an uplink channel of the UE, downlink channel quality information which the UE reports to the base station, feedback information (e.g., ACK/NACK information) of a Hybrid Automatic Repeat Request (HARQ) scheme, or buffer status information of the UE.
Specifically, the buffer status information of the UE will hereinafter be described in detail. The UE can transmit the buffer status information of the UE as for the L2 control information of the MAC layer to the base station. For this purpose, the buffer status information of the UE may be included in a MAC control element of the MAC PDU which is a data block of the MAC layer of the UE. In this case, the buffer status information of the UE may include information indicating an amount of data stored in the buffer of the UE. The MAC control element including the above buffer status information of the UE forms the MAC PDU along with a MAC header and without the MAC SDU corresponding to payload. So, the MAC control element may be transmitted to the base station, and may be carried on the MAC PDU according to a piggyback scheme and be then transmitted.
According to a representative method for enabling the base station to establish a UE-dedicated physical channel for only one UE, the base station may transmit allocation information of uplink radio resources, which will be allocated at intervals of a predetermined time, to the UE. The above allocation information of uplink radio resources will hereinafter be referred to as periodic radio resource allocation information. The UE can establish the UE-dedicated physical channel using this periodic radio resource allocation information.
In order to establish the UE-dedicated physical channel, a control message for establishing a UE-dedicated physical channel must be transmitted and received between the UE and the base station, such that system overhead occurs and an unexpected delay also occurs in the process for establishing the UE-dedicated physical channel.